Plants Cleverly Endure The Big Chill

As a warm-blooded creature, all I can conclude is that January is about basic survival.  Howling wind, falling snow and plunging mercury has my old house’s furnace working double-time.  I’m huddled under an afghan, counting on my laptop to keep me warm.  Perhaps it would be easier to go dormant like the plants outside, which are just as alive as me yet somehow better equipped to beat the chill.  So how can species such as oaks and maples, composed largely of water, survive double digit negative numbers while water itself freezes at a rather balmy 32 F?

For such woody plants, building up cold tolerance is a process.  Stage one hardiness is triggered by the shortening daylight and cooler temperatures of autumn, which stop growth, encourage the shedding of leaves, and trigger other chemical reactions which are not completely understood.  Just this decrease in light and temperature helps, allowing a stem to remain alive down to about 0 F, but no more.         

Next comes something called “deep supercooling.”  This ability to suppress the freezing of sap within plant cells is also somewhat of a mystery, but it allows many species to survive down to -40 F.  Part of the secret here are recently discovered “anti-freeze” proteins, which inhibit the growth and recrystallization of ice within the living part of the cells.  Certain animals can produce anti-freeze proteins, too, which led some scientists to insert an arctic flounder anti-freeze gene into sweet corn back in the ‘90’s, hoping to make a hardier crop.  While such tinkering with Mother Nature gives some people the chills, growing corn in Alaska would be super-cool.

The toughest of the tough – plants like paper birch, willow and red-twig dogwood – have another trick up their trunks to survive even colder conditions:  dehydration.  As temperatures plunge, water moves from inside the living cells into the dead cell walls, causing two good things to happen.  First, water freezing in the cell walls causes no harm to the plant, since the cells walls are dead.  Second, the sugars and other compounds inside the cell become concentrated, lowering the freezing point.  This parallels the practice of putting anti-freeze solution in car radiators, so your Dodge Aspen is more similar to a quaking aspen than you might otherwise think.   

Evergreen rhododendrons have a few tricks of their own, too.  They look pitiful when their leaves droop and curl on a frigid day, but it’s just a defense mechanism.  Rhodos loose water through stomates, tiny openings on the undersides of their leaves, and the drooping shelters stomates from the wind.  The trouble really starts when the soil freezes, cutting off the water supply from the roots, and causing browning of the foliage, a.k.a. winter injury, to occur.  But amazingly, some cultivars have even this figured out.  Rhododendron carolinianum ‘P.J.M.,’ one of the hardiest available, can lose up to 70% of its leaf moisture and be just fine, while the more tender Rhododendron catawbiense ‘Grandiflorum’ is injured when only 50% dehydrated.

Still shivering?  Pass the arctic flounder, please.

Getting A Head Start

Gardening guru Jerry Baker said plants were like people, and I believe seeds are, too.  Some seeds grow easily under many conditions, like your friend who thrives no matter what life gives her.  Similar to your black sheep cousin arriving on your doorstep, some seeds germinate unexpectedly by the back steps, in the driveway gravel, or in the compost pile.  Others are as fussy as your little sister, needing precise coddling to get moving.

This last group of seeds generally requires starting indoors well before planting out in the wide world.  The tiny print on the seed packet gently suggesting “start indoors eight to ten weeks before planting out” is a warning to plan ahead.  Other crops, such as tomatoes, germinate easily but take a good three months or more to fruit, so giving them a head start indoors assures production in the current calendar year. 

After assessing which seeds need what conditions, assemble your gear.  I like to use a soil-less mix, containing peat, perlite and vermiculite, specially formulated for seeds.  It’s lightweight, drains well, and contains no killer pathogens.  You can make your own mix, and even pasteurize it in your kitchen oven, but the stink and mess can substantially reduce household harmony.  I also use professional grade plastic cells, those familiar “six packs” seen in nurseries, but a wide array of food containers, cleaned and given drainage holes, may work just as well.  Containers can also be fashioned as soil blocks, made from peat or coir, or created from newspaper. 

Seedlings need light, a tricky proposition if you rely on a windowsill location here in sun-deprived upstate New York.  While the daylight is incrementally getting longer, cloudy days and low light intensity tend to leave seedlings spindly and weak.  Luckily, we’ve got artificial options.  Swanky “growing systems” with stands, trays, and lights are attractive, durable and easy to use.  Still, they’re too costly for thrifty me, who relies on classic “shop lights,” the four foot fixtures with two fluorescent bulbs.  Newer T-8 bulbs are longer lasting and more economical than the older T-12 type, while LED bulbs are more efficient still, and seedlings of most plant species will thrive under all of them.  Special “grow lights,” which produce more red and far-red light, are not needed for seedlings, but are a must if you’re trying to grow flowering plants under lights, such as African violets or orchids.

A swift kick in the bottom gets me motivated on Monday morning; a seed’s equivalent is bottom heat.  Put your seed tray on a heat mat, plug it in, and watch germination time drop as the seeds pop.  Put the tray on a warm surface – the top of the refrigerator or furnace – to get the same effect.  While many seeds will grow at normal room air temperatures, extra root-zone warmth helps.  The biggest danger is over-exuberance.  If your ‘Lemon Gem’ marigold packet advises six weeks start time, plant them on April 1, not February 1.  Seedlings get cabin fever just like the rest of us.        

Launching Potential

A new year and a packet of seeds:  both are full of promise.  This is what I think as I navigate around the four huge boxes of unsold seeds a large retailer gifted our Master Gardener group, which now sit in my office.  Seeds of vegetables from A to Z and flowers of every color give a gardener the starry eyes of a Christmas morning kid with ribbons to untie and boxes to unwrap.  And just about anyone can share in the magic of seeds.  Author Sue Stuart-Smith writes, “Gardening is more accessible than other creative endeavors, such as painting and music, because you are halfway there before you start; the seed has all its potential within it – the gardener simply helps unlock it.”

Some of these donated seeds are easy to grow, while others demand more coaxing.  Seed packet verbiage gives clues how to begin.  Something like “sow after all danger of frost has passed” means being patient until a dry, warm day in May, then heading outdoors with a shovel.  Instructions will hopefully also reveal how deep to plant the seed and how far apart from its neighbor it should go.  If planting in a row, some gardeners use two stakes and string to make a straight trench.  Directions for planting squash and their kin call for planting on a “hill,” which is just a slightly raised mound where you can install some seeds in a circular formation.  Mel Bartholomew, who introduced the world to his “square foot gardening” method, encouraged growing vegetables in a grid pattern, and his books are well worth reading, especially if you grow in raised beds.  Seed spacing is more important than your overall pattern, since seeds sown too closely will become overcrowded seedlings if the germination rate is high.  While you can always thin them, by plucking out the extras and leaving a chosen few, doing your best to space properly reduces wastage and that guilty feeling of uprooting innocent creatures.

By walking outside and sticking a seed in the soil, you are participating in the “direct sowing” method.  A wide variety of plants, from pumpkins and carrots to marigolds and zinnias, can be started this way.  Most will desire full sun but will tolerate some shady times of the day.  Most will prefer soil which drains well but still retains some moisture – something between beach sand and pottery clay.  Checking the pH, adding compost and giving the soil some fertilizer are all things, as a professional horticulturist, I am supposed to direct you to do, with good reason, as generally the plants grow better.  But sometimes professional advice can turn into obstacles, and I would much rather see people plant a garden and experience their results than get overwhelmed and stuck by too many rules at square one.  You can always contact us at Extension if things go wonky.

If you work with a school or community group and need vegetable and flower seeds, email me at dhc3@cornell.edu and maybe we can help.